Tonight the ink disk got machined. There was significant run-out, although not as bad as it looked when we put the straight edge across it. There is something about the light coming through that little gap formed by the straight edge and the surface being checked that really amplifies any error.
The gap looked huge, but on the lathe with a dial indicator it "only" measured 0.020". In any case, to get a decent cut and a feed rate without chatter resulted in 0.030" being taken off the ink surface. A big deal was to have secondary support at the ratchet ring to the lathe chuck. Before that the cutting tool action on the disk was just screeming with vibration. The surface is not perfect, but it is perfectly flat and I can polish the rest in position on the press. Now I've got to get myself a machinist straight edge so that I can measure if the disk sits too low, and if I have to make up a bronze washer for the bearing to bring it up the 0.030" that it was sitting higher before.